The Section on Developmental Gastroenterology and Nutrition was established to study the cellular events leading to differentiation. The desirable model for this study is the intestinal epithelium because in a short period of time (48 hours), the undifferentiated crypt cell undergoes proliferation, migration, and differentiation. This orderly sequence of events in the jejunum of the fetal rabbit provides a convenient investigative model. A dissociation method has been devised using citrate and EGTA to isolate differentiated and undifferentiated intestinal epithelial cells. Differentiation gradients from crypt to villus are biochemically demonstrated by increasing levels of dissacharidases and ornithine carbamyl transferase. Thymidine kinase levels to evaluate cellular proliferation demonstrate increased activity at the undifferentiated cell level, but are not specific for intestinal cells. We are seeking by immunologic methods a good marker to identify the undifferentiated intestinal epithelial cell. The laboratory is presently attempting to establish these cells in tissue culture.